U.S. Patent Publication No. 2012/0034150 A1, published Feb. 9, 2012, the disclosure of which is hereby incorporated herein in its entirety by this reference, discloses background information hereto.
Additional information is disclosed in the following documents, listing Dallas B. Noyes as inventor, the disclosure of each of which is hereby incorporated herein in its entirety by this reference:                1. International Application No. PCT/US2013/000072, filed on even date herewith, for “Methods and Structures for Reducing Carbon Oxides with Non-Ferrous Catalysts,” which claims the benefit of U.S. Ser. No. 61/624,702, filed Apr. 16, 2012;        2. International Application No. PCT/US2013/000077, filed on even date herewith, for “Methods for Producing Solid Carbon by Reducing Carbon Dioxide,” which claims the benefit of U.S. Ser. No. 61/624,723, filed Apr. 16, 2012;        3. International Application No. PCT/US2013/000073, filed on even date herewith, for “Methods and Reactors for Producing Solid Carbon Nanotubes, Solid Carbon Clusters, and Forests,” which claims the benefit of U.S. Ser. No. 61/624,753, filed Apr. 16, 2012;        4. International Application No. PCT/US2013/000075, filed on even date herewith, for “Methods for Treating an Offgas Containing Carbon Oxides,” which claims the benefit of U.S. Ser. No. 61/624,513, filed Apr. 16, 2012;        5. International Application No. PCT/US2013/000071, filed on even date herewith, for “Methods for Using Metal Catalysts in Carbon Oxide Catalytic Converters,” which claims the benefit of U.S. Ser. No. 61/624,848, filed Apr. 16, 2012;        6. International Application No. PCT/US2013/000081, filed on even date herewith, for “Methods and Systems for Capturing and Sequestering Carbon and for Reducing the Mass of Carbon Oxides in a Waste Gas Stream,” which claims the benefit of U.S. Ser. No. 61/624,462, filed Apr. 16, 2012;        7. International Application No. PCT/US2013/000078, filed on even date herewith, for “Methods and Systems for Forming Ammonia and Solid Carbon Products,” which claims the benefit of U.S. Ser. No. 61/671,464, filed Jul. 13, 2012; and        8. International Application No. PCT/US2013/000079, filed on even date herewith, for “Carbon Nanotubes Having a Bimodal Size Distribution,” which claims the benefit of U.S. Ser. No. 61/637,229, filed Apr. 23, 2012.        
Solid carbon has numerous commercial applications. These applications include longstanding uses such as uses of carbon black and carbon fibers as a filler material in tires, inks, etc., many uses for various forms of graphite (e.g. electrodes, pyrolytic graphite as heat shields) and innovative and emerging applications for buckminsterfullerene and carbon nanotubes. Conventional methods for the manufacture of various forms of solid carbon typically involve the pyrolysis of hydrocarbons in the presence of a suitable catalyst. The use of hydrocarbons as the carbon source is due to historically abundant availability and low cost of hydrocarbons. The use of carbon oxides as the carbon source in the production of solid carbon has largely been unexploited.
Carbon oxides, particularly carbon dioxide, are abundant gases that may be extracted from point source emissions such as the exhaust gases of hydrocarbon combustion or from some process off gases. Carbon dioxide may also be extracted from the air. Because point source emissions have much higher concentrations of carbon dioxide than air, they are often economical sources from which to harvest the carbon dioxide. However, the immediate availability of air may provide cost offsets by eliminating transportation costs through local manufacturing of the solid carbon products from carbon dioxide in air.
Carbon dioxide is increasingly available and inexpensive as a byproduct of power generation and chemical processes where an object may be to reduce or eliminate the emission of carbon dioxide into the atmosphere by capture and subsequent sequestration of the carbon dioxide (e.g., by injection into a geological formation). For example, the capture and sequestration of carbon dioxide is the basis for some “green” coal-fired power stations. In current practice, capture and sequestration of the carbon dioxide entails significant cost.
There are a limited number of ways that carbon, oxygen, and hydrogen can react. There is a spectrum of reactions involving these three elements wherein various equilibria have been identified. Hydrocarbon pyrolysis involves equilibria between hydrogen and carbon that favors solid carbon production, typically with little or no oxygen present. The Boudouard reaction, also called the “carbon monoxide disproportionation reaction,” is the range of equilibria between carbon and oxygen that favors solid carbon production, typically with little or no hydrogen present. The Bosch reaction is within a region of equilibria where all of carbon, oxygen, and hydrogen are present under reaction conditions that also favor solid carbon production.
The relationship between the hydrocarbon pyrolysis, Boudouard, and Bosch reactions may be understood in terms of a C—H—O equilibrium diagram, as shown in FIG. 1. The C—H—O equilibrium diagram of FIG. 1 shows various known routes to solid carbon, including carbon nanotubes (“CNTs”). The hydrocarbon pyrolysis reactions are on the equilibrium line that connects hydrogen (H) and carbon (C) (i.e., the left edge of the triangle). The Boudouard, or carbon monoxide disproportionation reactions, are on the equilibrium line that connects oxygen (O) and C (i.e., the right edge of the triangle). The equilibrium lines for various temperatures that traverse the diagram show the approximate regions in which solid carbon will form. For each temperature, solid carbon may form in the regions above the associated equilibrium line, but will not generally form in the regions below the equilibrium line.
U.S. Pat. No. 7,794,690 (Abatzoglou et al.) teaches a dry reforming process for sequestration of carbon from an organic material. Abatzoglou discloses a process utilizing a 2D carbon sequestration catalyst with, optionally, a 3D dry reforming catalyst. For example, Abatzoglou discloses a two-stage process for dry reformation of an organic material (e.g., methane, ethanol) and CO2 over a 3D catalyst to form syngas, in a first stage, followed by carbon sequestration of syngas over a 2D carbon steel catalyst to form CNTs and carbon nanofilaments. The 2D catalyst may be an active metal (e.g., Ni, Rh, Ru, Cu—Ni, Sn—Ni) on a nonporous metallic or ceramic support, or an iron-based catalyst (e.g., steel), on a monolith support. The 3D catalyst may be of similar composition, or may be a composite catalyst (e.g., Ni/ZrO2—Al2O3) over a similar support. Abatzoglou discloses preactivation of a 2D catalyst by passing an inert gas stream over a surface of the catalyst at a temperature beyond its eutectic point to transform the iron into its alpha phase. Abatzoglou teaches minimizing water in the two-stage process or introducing water in low concentrations (0 to 10 wt %) in a reactant gas mixture during the dry reformation first stage.
It would be desirable to have new methods and systems for forming solid carbon. It would further be desirable if the new methods and systems were energy efficient, cost efficient, and relatively simple in operation.